Various perishable, harvested materials, including fruits and vegetables, pass through several changes which eventually terminate with full maturity, senescense or deterioration. Many of these changes continue after harvesting, namely, the time at which the fruit, vegetable or floral is severed from the living plant which brought it into being. Postharvest events particularly relate to the normal physiological evolution of the produce which is continued, at least in kind, if not quantity, originally from the natural energy source (the rooted plant), but which continues even after harvesting. In the beginning, there is cellular growth and expansion. These growth stages are described in many ways, one typical mode of description being found in Kreb's Cycle, relating to the conversion of starches to sugars. Other variables entering into the growth of a plant and, particularly, the fruit thereof include sunlight, moisture, nutrients derived from the soil, atmospheric constituents, pollution components regrettably in the air, chemical fertilizers and the like. These factors have a direct impact on the growth of the fruit preharvest which entails the multitudinous physiological changes that take place in the fruit. Many of these changes are keynoted by respiration of the perishable as physiological changes occur within, and this continues even after harvesting. It will eventually terminate only after passage of full maturity, perhaps subsequent decay or rotting, presuming that the fruit is not harvested in some usable fashion.
Factors which impact the development of the perishable during the initial stages are also important in typical postharvest circumstances. Without attempting to be too specific with regard to all fruits, vegetables and florals, there are three relatively common factors which come into play in maintaining continued quality of the perishable after it has been harvested. These three factors in all relate to the interplay between the harvested perishable and the nearby atmosphere. The factors are the respiration rate of the fruit, the ambient temperature and the ambient relative humidity. All factors are interdependent on one another. While a general rule cannot be developed which will describe the relationship of these three variables to all perishables, and, indeed, different perishables may act in contrary fashion to other perishables, the generalization nevertheless remains true that these factors are important in the postharvest deterioration, through maturing, senescenese or deterioration, of the invitation of mold or fungi development.
There exists for a typical perishable optimum conditions of respiration rate, temperature and relative humidity in postharvest conditions which will enable the fruit, vegetable or floral to delay or avoid the onset of decay, premature deterioration or premature maturation.
In postharvest conditions, respiration of the perishable permits various hydrocarbon gases to escape from the perishable Interestingly, some of the evolved gases either accelerate or delay aging, mold or fungi development of the perishable. The gases are relatively complex, being a mixture of many specific gases, but, in the main, carbon dioxide is notably present, and the most important evolved gas is ethylene. Ethylene is, thus, emitted from a postharvest perishable and is further a ripening hormone and, therefore, plays a specific role in postharvest perishable deterioration and decay. The present disclosure is concerned with evolved ethylene, not ethylene from petrochemical processing plants or naturally occurring ethylene from other sources. The ethylene of interest is that which is naturally synthesized within a perishable and which flows through the permeable surface of the perishable. Sometimes, the ethylene will materialize from the very beginning of the life of the fruit, and, in other instances, it will occur only after various precursors have occurred. A typical, although not singular, precursor is methionine. Other precursors occurring within the perishable include lanolinic acid, fructose, acidaldehyde, pyruvic acid and others.
It has been documented by various projects investigating the impact of ethylene on postharvest perishables that ethylene can readily initiate ripening, exudation, budding, root elongation (as in tubers), abscission, chlorophyll degradation, degreening, spore germination, alteration of pollination and other responses in a variety of perishables in preharvest circumstances. The quantity of ethylene (on a basis of ethylene evolved per kilogram of perishable material) is, in large part, a function of ambient air temperature and air relative humidity. It is also, of course, a function of the genus and species of the plant in question. Accordingly, some plants are high sensitive to very minute concentrations of ethylene which will trigger an ethylene-related response, while other plants are more highly tolerant to concentrations of ethylene in the near atmosphere. It is believed that there must be actual impingement on the fruit of the ethylene to initiate the actions which are referenced here.
Other factors impact the trace quantity of ethylene required to initiate a given response in a specific perishable. A variety of these factors include whether or not the plant, itself, is healthy, whether or not it has damaged or decaying tissue, the presence or absence of insect damage and so on. Another important factor is the amount of carbon dioxide in the air. Carbon dioxide is something of a deterrent to ethylene production within the perishable and, hence, ethylene respiration in the near atmosphere around the perishable. An increase in the carbon dioxide level lowers the ethylene level; the reverse is also true within specified limits. It might be further noted that another important variable is the classification of the perishable as a climacteric or nonclimacteric perishable. As a result of these highly interconnected variables for a given perishable, the ethylene respiration is not fixed, but is a variable which is at least typically peaked and subject to a decline, otherwise. As ethylene gas is respirated towards a peak flow rate from an ultimately mature fruit, it is accompanied by internal deterioration of the perishable. This is made visible on the exterior by, perhaps, breaks in the skin, shriveling on the surface, discoloration or markings on the peel and the like. This may also be accompanied by decay organisms which are deployed at or near damaged areas. Indeed, an aging perishable suffers from enhanced development of mold and fungi at the damaged tissue as a function of ethylene concentration. More importantly, once mold and fungi begin to form, they initiate the production of even more ethylene so that the process becomes a runaway whereby additional ethylene respiration compounds the already initiated aging process. These facts are believed to be well documented by researchers who have established that there is a direct correlation between the maturity of perishables and the propensity of decay organisms to develop and particularly so during the late maturity stages.
The above sequence can be described as, in part, dependent on two factors which are (1) the prevention or retardation of the maturing process of the perishable, and (2) alteration of the natural or near atmosphere conditions to discourage decay and decline.
The present invention is able to control concentrations of respiration gases in the near atmosphere of perishables in postharvest conditions. It is accomplished in light of the typical commercial circumstances of handling various harvested materials. Harvested produce, including fruits, vegetables and florals, are customarily boxed and then shipped in closed cargo containers. In many instances, they may be refrigerated, but this does not detract from the fact that they comprise a closed and often sealed container. It is customary in the fresh produce industry to utilize vented wooden crates, slotted fiber or cardboard boxes or other equivalent packaging. Occasionally, types of bags, including insulated or wax-coated bags, will be used, and these have absolutely a minimum of circulation or ventilation capacity. It has been noted that the particular mode of packaging will vary, and it depends on the nature of the crop in question. In any case, postharvest fruit, vegetables and florals have a specific time interval permitted before the perishable product is in danger. This time is shortened by meager ventilation. Ventilation, however, is very difficult in some circumstances where the container is a closed bag with no ventilation. Ventilation is not very good either in a closed freight car, with or without air conditioning equipment. The question of ventilation cannot be decided by considering evolution of ethylene gases, only. In other words, the near atmosphere concentration of ethylene gas is very important, but that factor cannot be dealt with singly. As an example, many postharvest fruits, vegetables or florals require a closed system which captures and maintains substantial moisture in the air to have high moisture content within the fruit. This is necessary to prevent dehydration. Thus, many produce products must be shipped in closed or nonventilated boxes. In that instance, cooling the air does not dry the air or reduce the moisture content near the product.
As a consequence of the foregoing factors, more often than not, postharvest perishables are shipped utilizing storage and shipping containers which may be described as closed systems. Very few exceptions occur, but they include such things as cantaloupe and watermelons, which can be shipped in open trucks. They are, however, characterized by very thick skin or rind. A closed system is typified by cold storage room, a closed truck with or without refrigeration equipment, freight cars, banana boats, air freight containers and the like. During both shipping and storage, the closed nature of the system constrains the variables mentioned above, namely, respiration, temperature and relative humidity. This creates short and long-term problems. Inevitably, the respiration and transpiration of the postharvest perishable continues substantially unabated. Because the respiration occurs within a closed container system, the evolved gases from the perishable are captured and accumulate. Because an accumulation of ethylene occurs, and further because ethylene, carbon dioxide and other typical evolved gases are immediately nearby, and further in light of the stimulative effect thereof, the metabolism rate of the perishable is typically accelerated. This has many manifestations. An exemplary manifestation is achieved in a cold storage room holding mature, green tomatoes, along with other ethylene-emitting perishables. The ethylene produced by other products will induce a maturing response in the green tomatoes which will accomplish a color change which, perhaps, is undesirable in the green tomatoes.
The example mentioned above is not a limitation on the problem. The problems encountered in closed system storage of perishables are broader and more difficult than would be implied by the example cited above. More importantly, laboratory tests and actual field conditions have indicated that the associated decay, fungi or mold development are manifestations which typically require either culling and quick conversion of the product or destruction of the entire cargo should the senescense proceed beyond a specified point. This has been combated by various systems known heretofore in the literature, and it is further combated through the use of more expensive, high speed transportation techniques. High speed transportation inevitably costs more money than slow speed transportation. The present invention, in large part, overcomes these problems and particularly provides a means and apparatus which can be tailored to combat the evolution of gases from maturing produce in a closed system, or elsewhere. The present apparatus and method adsorb, oxidize and filter out certain airborne contaminants to thereby avoid ideal conditions for accelerated maturity and senescense, coupled with a suppression of decay, mold and fungi development.
The disclosure herein describes a compartmentalized air filtration apparatus ideally used in the immediate or adjacent atmosphere of a closed or open container of perishables. The perishables, subject to normal metabolic or physiological maturation, typically involve hydrocarbon gases which remain in the immediate near atmosphere momentarily. This invention reduces the concentration of these gases to a specified level, thereby impeding maturation and senescense of the produce. The disclosed apparatus thus comes in a multiplicity of sizes, ideally, a small packet for placing in a cardboard carton of produce and a larger construction to be placed in a larger container.